Head worn miniature hearing aids have been provided with a directionality feature in recent years so as to provide relatively greater amplification of sounds originating from sources in front of the person wearing the aid as compared with sounds originating generally behind the person.
The directionality feature is obtained through the use of a directional microphone in the miniature head worn hearing aid unit. Such a directional microphone has a diaphragm confined within a case which has a front sound port and also a rear sound port providing a significant acoustic resistance. Various factors have been found to influence the degree of directionality obtained through the use of such a hearing aid unit containing a directional microphone. Such factors include the magnitude of the acoustic resistance at the rear port of the microphone; other acoustic resistance within the hearing aid housing between the microphone ports and the atmosphere at the exterior of the openings in the hearing aid housing; the total length of the acoustic path from one face of the microphone diaphragm to the other face of the diaphragm; the size of the chamber within the microphone between the diaphragm and the acoustic resistance; and the frequencies of the sounds of dominant interest to the person wearing the aid.
By varying the physical dimensions of the microphone and the hearing aid housing the directivity of the hearing aid may be changed, and, if desired, may be increased.